In the conventional design of the backhoe, there is a transport position that is characterized by a generally vertically and slightly rearwardly extending boom carrying a folded dipper stick as close as possible to the boom so as to position the center of gravity of the backhoe as near as possible to the rear end of the tractor or machine upon which it is mounted. Typically the center of gravity of the backhoe is approximately 42 inches to the rear of the mounting pivots for the swing tower. This relationship is not conductive to stability and handling especially when the backhoe is moved at high speeds over the open road.
One particular advanced backhoe design incorporates an arrangement wherein the center of gravity for the backhoe is substantially closer to the rear of the tractor upon which it is mounted. That design incorporates an "overcenter movement" of the hydraulic actuator or boom cylinder manipulating the boom when the boom is swung to its transport position. In the transport position, the backhoe has a generally vertically and slightly forwardly extending boom held in a "knee lock" by the boom cylinder which has gone overcenter. This design has received wide acceptance by the industry and is the subject of U.S. Pat. No. 3,376,984 which is assigned to the assignee of the present invention. Although the aforementioned backhoe design by Long represents a significant improvement, further improvements in efficiency and productivity should be possible.
When a backhoe implement is attached to the rear end of a tractor or similar machine, the tractor operator reverses his position on the tractor to operate the backhoe so as to face the rear of the tractor where the controls for the backhoe implement are mounted. Since the shovel or scoop end of the backhoe is pivoted so as to fold towards the dipper stick and since the dipper stick is pivoted to fold towards the boom of the backhoe, the boom effectively obscures the tractor operator's view of the dipper stick, and more significantly, the inside of the bucket.
Moreover, it has been conventional practice to operate the boom of the backhoe by hydraulic actuators or cylinders which are positioned to either side of the boom. Thus, for the most part the tractor operator's direct line of sight to the bucket is shielded by the boom and the boom cylinders. For example, the overall width of the backhoe boom is generally about 6 inches and the overall width of each hydraulic actuator or cylinder is on the order of 4.5 inches. Thus, in ordinary backhoes, a barrier of approximately 15 inches is interposed between the backhoe operator and the bucket.
There are many times during the operation of a backhoe when the backhoe operator's view of the bucket is crucial. This is particularly true when the bucket is being manipulated at close quarters to another worker or helper or when the backhoe bucket is being moved or positioned at closes quarters to equipment or scaffolding which could be easily damaged due to movement of the bucket.
In addition, the conventional practice of flanking the boom by two hydraulic actuators or cylinders can lead to maintenance problems and equipment difficulties. This is true because the hydraulic actuators for the backhoe boom are relatively weak compared to the boom. This is particularly true when the hydraulic actuators are fully extended and a force is imposed between its ends that is generally perpendicular to the longitudinal axis of the actuator. This is an inherent characteristic of hydraulic actuators because they are used to produce force in the direction of their longitudinal axis. The only resistance against motion perpendicular to the longitudinal axis of the actuator is that provided by the seals on the piston and those between the piston rod and the cylinder. Comparatively speaking, the boom is a relatively strong structure and can easily resist forces or thrusts imposed laterally on the boom. Thus, if the boom is flanked by two hydraulic actuators, it cannot be used to protect those actuators from lateral forces such as those which would be experienced when the boom is inadvertently swung against the walls of a deep narrow trench.
Finally, it should be appreciated that any reduction in weight, any simplification in the manner in which the various components of the backhoe are linked together, and any improvement of the overall design of the backhoe would go far to reduce the production costs of the backhoe and the expense of maintaining the backhoe while improving the overall productively of the machine. A design change that accomplishes all of these objections would be well accepted by the industry.